LT6003 datasheet(19/30 Pages) AD

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LTC2066/LTC2067/LTC2068

Rev. B

For more information www.analog.com

APPLICATIONS INFORMATION

There are benefits when the SHDN pin is used to disable

and enable the part in duty-cycled applications, rather

than powering down the external supply voltage (V+).

Powering up and powering down the external supply will

tend to waste charge due to charging and discharging the

external decoupling capacitors. For these power-cycled

applications, a relay or MOS device can be located after

the decoupling capacitors to alleviate this; however there

are drawbacks to this approach. The LTC2066 draws an

initial charge of approximately 3nC when powered up.

This recurring charge loss is unavoidable in power-cycled

applications. Additionally, if the supply ramp rate exceeds

0.4V/µs, an internal transient ESD clamp will trigger, con-

ducting additional current from V+ to V–. This will waste

charge and can make insignificant any savings that may

have been expected by power-cycling the supply. Figure 8

shows the charge loss at power-up.

The shutdown pin can be used to overcome these limita-

tions in duty-cycled applications. The typical charge loss

transitioning into and out of shutdown is only 2.3nC.

Since the supply is not transitioned, the external decou-

pling capacitors do not draw charge from the supply.

SUPPLY EDGE RATE (V/µs)

0.1

100

2066 F08

Figure 8. LTC2066 Power-Up Charge vs Supply Edge Rate

Gas Sensor

This low power precision gas sensor circuit operates in

an oxygen level range of 0% to 30%, with a nominal out-

put of 1V in normal atmospheric oxygen concentrations

(20.9%) when the gas sensor has been fully initialized.

Total active power consumption is less than 10.1μA on a

single rail supply.

Since this gas sensor produces 100μA in a normal oxy-

gen environment and requires a 100Ω load resistor, the

resulting input signal is typically around 10mV. The

LTC2066’s rail-to-rail input means no additional DC level

shifting is necessary, all the way down to very low oxygen

concentrations.

Due to the extremely low input offset voltage of the

LTC2066, which is 1μV typically and 5μV maximum, it is

possible to gain up the mV-scale input signal substantially

without introducing significant error. In the configuration

shown in Figure 9, with a noninverting gain of 101V/V, the

worst-case input offset results in a maximum of 0.5mV

offset on the 1V output, or 0.05% error.

Although the 100kΩ resistor in series with the gas sen-

sor does not strictly have the same precision requirement

as the 10MΩ and 100kΩ resistors that set the gain, it is

important to use a similar resistor at both input terminals.

This helps to minimize additional offset voltage at the inputs

due to thermocouple effects and bias current, hence the

similar 0.1% precision requirement.

Figure 9. Micropower Precision Oxygen Sensor

100k*

0.1%

100

0.1%

100k

0.1%

10M

0.1%

OXYGEN SENSOR

CITY TECHNOLOGY

40XV

VOUT = 1V IN AIR

ISUPPLY = 7.5µA (ENABLED)

90nA (SHUTDOWN)

www.citytech.com

VSHDN

*RESISTOR CANCELS OUT PARASITIC SEEBECK EFFECT VOLTAGE

2066 F09

1.8V

LTC2066

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